Question about quality of hand drawn image

Hello community! I use Adobe products every day, but I am not very active on Stock so I am not sure what was wrong here. This is a hand drawn phone wallpaper - I drew it in Procreate using symmetry.  I did have to use Photoshop to upscale it because I make my wallpapers (for other places) at 1440x2560.  When I went to upload, it failed to upload due to being too small on the resolution.  I didn’t use the AI in photoshop to upscale it, I went the old fashioned way in Photoshop.  It’s not an AI image so I didn’t want to use AI to upscale it.  I brought it up to 2160x3840 and changed it to 300 DPI from 72 (I usually do phone wallpapers at 72.) 

Maybe it is just something they don’t like, but it is original and hand drawn.  The issue stated was a quality issue.  I will be selling it other places so it’s not a big deal for me, just wondering what the problem is here with this one.  Do you think it is just the style? Under quality is lists over exposure and other stuff, but this is hand drawn lol.  It was a random doodle one night and I decided to add color and my daughters loved it.

 The file size is too large for me to upload the 2160x3840 picture in this post, but this is the original 1440x2560.